Controlling Japanese beetles in the landscape
by Jo Ellen Meyers Sharp
From late June into early August, Japanese beetles turn luscious leaves in the landscape into lacy leftovers. These attractive, metallic green imports feed on more than 300 species of leaves, flowers and fruit, including hibiscus, apples and roses.
First discovered in New Jersey in the early 1900s, the imports have made it all the way to Minnesota, munching on plants and reproducing along the way. The half-inch-long beetle with copper-colored wings is the most visible form of the insect's life in the Midwest. The adult beetles transform from a white larva, commonly called grubs, found in the soil under the grass and sometimes in garden beds.
Female adult beetles burrow into the ground to lay eggs in summer. The eggs hatch into grubs, which feed on grass roots. The grubs stay underground, pupate and emerge the following summer as beetles. Grubs are considered a serious lawn pest. One sign of a grub infestation are patches of dead grass, observable in spring or sometimes in fall, says Jim Roberts, owner of highly rated Watershed Organic Lawn Care in Columbus, Ohio. It's this sign that prompts people to call for help before they're eyewitness to Japanese beetles on plants.
To test if your lawn has grubs, Roberts recommends lifting a 12-inch square piece of sod and count the number of grubs you find. If you have eight to 12 grubs per square foot, the area should be treated. His organic approach to eradicating the pests relies on biological and natural weapons. His arsenal includes:
- Milky spore, a bacterial disease of beetle larvae. It's applied to the lawn as a powder and is effective against grubs for 10 to 15 years.
- Beneficial nematodes, microscopic insect-like creatures, dine on grubs. They're mixed with water and applied to the lawn and remain effective for about a year.
- Bacillus thuringiensis, a bacteria that kills Japanese beetle grubs for about a year.
Sometimes homeowners are prompted to action because the beetles are devouring a beloved tree, says Tom Tyler, a certified arborist with highly rated Bartlett Tree Experts in Woodridge, Ill. "If the damage is severe enough, certain trees will appear brown and aesthetically unpleasing," he says. "There's nothing we can do to repair the damage done during the growing season."
A tree that is seriously damaged for several years in a row may eventually weaken. For the most effective treatment, Tyler recommends waiting until the fall before applying a preventive insecticide. The insecticide kills the beetles that eat the leaves the following year. A treatment for a single tree may cost $100 to $250 or more, depending on its location and size.
Tyler, Roberts and other experts suggest homeowners avoid Japanese beetle traps. The traps use pheromones as bait, or scents that attract Japanese beetles. They're so effective that they attract more beetles than normal. And the bugs dine on your plants along the route as they fly to the trap.
Sometimes known as the Hoosier Gardener, Jo Ellen Meyers Sharp lives in Indianapolis, where she manages perennials and woody plants for a large, independent garden center. A freelance writer, her work appears in many publications, including The American Gardener and Garden Gate. Sharp also speaks about gardening throughout the Midwest and is a director of the Garden Writers Association.